Sex pheromones of insects are each a biologically active substance typically released from female individuals and having a function of attracting male individuals. They exhibit highly attractive activity even in small amounts. Sex pheromones have been used widely as means for forecasting the emergence or confirming geographical distribution (invasion into a specific area) of insect pests, or means for controlling insect pests. The means for controlling insect pests includes mass trapping, lure & kill or attract & kill, lure & infect or attract & infect, and mating disruption, which have been widely provided in practical use. Upon using sex pheromones, production of a necessary amount of each of the synthetic sex pheromones at a low cost is may be needed for basic research and moreover, for application.
A Japanese mealybug, Planococcus kraunhiae is an economically important insect pest distributed in Japan, China, Eritrea, and North America since it causes damage to many kinds of fruits. Sugie, et al., isolated the sex pheromone of this insect. The sex pheromone thus isolated coincided, in various spectra, with a compound (which is described as Compound A in the document) obtained in a yield of 0.2% under the acidic condition of the esterification reaction of 2-isopropenyl-5-methyl-4-hexenol (lavandulol) with butyryl chloride, and also various spectra coincided between their derivatives. As a result, the sex pheromone was determined to be 2-isopropylidene-5-methyl-4-hexenyl butyrate (fujikonyl butyrate) (App. Entomol. Zool., 43, 369-375(2008)).
Control of the Japanese mealybug using mating disruption is expected to be promising because of difficulty in conventional control using a pesticide. For fundamental biological research or agricultural research and moreover, for providing for application or practical use, a sufficient amount of synthetic pheromone should be supplied. There is therefore an eager demand for the development of a highly efficient and highly selective production method in which an amount of isomeric byproduct is small so that no purification is required.
Tabata has reported the synthesis of 2-isopropylidene-5-methyl-4-hexenyl butyrate in which 2-isopropenyl-5-methyl-4-hexenol as a starting material is subjected to an oxidation reaction with Dess-Martin reagent to form 2-isopropenyl-5-methyl-4-hexenal (lavandulal), the resulting aldehyde is isomerized under an acidic condition through migration of the double bond to form 2-isopropylidene-5-methyl-4-hexenal (another name: fujikonal), and the isomerized aldehyde is reduced and then esterified to form 2-isopropylidene-5-methyl-4-hexenyl butyrate (Appl. Entomol. Zool., 48, 229-232 (2013)).